<script src='jquery-3.5.1.slim.min.js'></script>
<style>
.highlight {
    color: #dd1144;
    background-color: #ffd351;
}
</style>

<div id="test-highlight-css">
    <ul>
        <li class="py"><span>Python</span></li>
        <li class="js"><span>JavaScript</span></li>
        <li class="sw"><span>Swift</span></li>
        <li class="hk"><span>Haskell</span></li>
    </ul>
</div>
<p>Gender: 
    <label><input name="gender" type="radio" value="m" > Male</label> 
    <label><input name="gender" type="radio" value="f"> Female</label>
    <label><input name="gender" type="radio" value="lgbt"> LGBT</label>
</p>
<button onclick="test()">RUN SCRIPT</button>

<input id="test-input" name="email" value="">
<select id="test-select" name="city">
    <option value="BJ" selected>Beijing</option>
    <option value="SH">Shanghai</option>
    <option value="SZ">Shenzhen</option>
</select>
<textarea id="test-textarea">Hello</textarea>

<div id="test-div">
    <ul>
        <li><span>JavaScript</span></li>
        <li><span>Python</span></li>
        <li><span>Swift</span></li>
    </ul>
</div>

<script>
function test()
{
    var div = $('#test-highlight-css');
    div.find('.js').addClass('highlight');
    //hasClass, removeClass
    div.find('.sw').css('color', '#dd1144');
}

</script>